You're looking at the Afar Depression in Ethiopia, a 12-foot-wide hot springs that exists at the junction of three massive tectonic plates. It also sits on top of a volcano.

This photo was taken by Carsten Peter for National Geographic. The magazine explains:

[In the Afar Depression,] spreading mid-ocean ridges forming the Red Sea and the Gulf of Aden emerge on land and meet the East African Rift.

Those circular structures around the pool are made of travertine, which is "a volcanically heated, calcium-rich flow from hot springs." Want to see a bigger version of this photo, plus several more images of what happens to the land at the edges of tectonic plates? Check out the photo essay at National Geographic.